Approximately 75% of breast cancers are estrogen receptor (ER) positive. Other cancers are also ER positive (ER+). Estrogen receptors mediate intracellular signaling that can increase the frequency of cell division and drive tumor growth. Although anti-endocrine therapies such as tamoxifen, fulvestrant, and letrozole have demonstrated significant efficacy in treating ER+ breast cancer patients, intrinsic or acquired resistance to such therapies has limited their success.
The prevalence of amplification of the human epidermal growth factor receptor 2 (HER2, or ErbB2) in breast cancer and other cancers has resulted in the research and development of drugs that have ErbB2 as a therapeutic target. Although both the anti-ErbB2 monoclonal antibody trastuzumab or TMD1 and the ErbB1/ErbB2 dual receptor tyrosine kinase inhibitor lapatinib have met with success in the clinic, many patients fail to benefit from these drugs. Additionally, the majority of patients with tumors that initially respond will eventually recrudesce after extended treatment using these therapies.
The ErbB2/ErbB3 heterodimer is the most potent ErbB receptor pairing with respect to strength of interaction, impact on receptor tyrosine phosphorylation, and effects on downstream signaling through mitogen activated protein kinase and phosphoinositide-3 kinase pathways. Heregulin is the primary ligand for ErbB3, and activates signaling by ErbB2/ErbB3 heterodimers. Current ErbB2-targeted therapies do not effectively inhibit heregulin activated signaling. MM-111 is a bispecific anti-ErbB2/anti-ErbB3 antibody that abrogates heregulin binding to ErbB2/ErbB3 and inhibits heregulin activation of ErbB2/ErbB3 without significantly affecting ErbB2 biological activity. In preclinical models of HER-2+ gastric, breast, ovarian and lung cancers, MM-111 inhibits ErbB3 phosphorylation, cell cycle progression, and tumor growth.
Thus, a need exists for therapies and therapeutic strategies providing improved inhibition of ErbB3 activation (e.g., ligand-induced activation) as well as for therapies and therapeutic strategies providing improved inhibition of estrogen receptor signaling activity or of ErB1 and ErbB2 receptor signaling activity.
In the treatment of cancers, the co-administration of pluralities of anti-cancer drugs (combination therapy) often provides better treatment outcomes than monotherapy. Such outcomes can be subadditive, additive, or superadditive. That is to say that the combined effects of two anti-cancer drugs, each of which provides a quantifiable degree of benefit, can be less than, equal to, or greater than the sum of the benefits of each drug. For example, two drug, each of which when used alone to treat a lethal cancer provides an average one year extension of progression free survival, could together provide a <24 month extension (e.g., an 18 month extension), about a 24 month extension, or a >24 month extension (e.g., a 30 month extension) of progression free survival. Typically, combination therapies for cancer treatment provide significantly subadditive outcomes. Outcomes that are near additive, additive, or superadditive are most desirable, but only occur rarely. In addition, many drugs are known to alter the bioavailability, or otherwise affect the safety profile of other drugs when both drugs are co-administered. As new drugs are first used in combination therapies, unforeseen, hazardous drug-drug interactions may be observed that result in drug-drug interaction-mediated toxicity in the patient.
Thus approaches for safely administering combination therapies comprising administration of ErbB2/ErbB3 heterodimer-targeted agents for cancer treatment, and especially combinations that yield near-additive, additive, or superadditive outcomes are needed.